View unanswered posts | View active topics It is currently Tue Dec 18, 2018 11:35 am



Reply to topic  [ 33 posts ]  Go to page Previous  1, 2, 3, 4  Next
Bosch LSU 4.x controller from Arduino / Maple or similar 
Author Message
TO220 - Visibile

Joined: Mon Sep 03, 2012 8:48 pm
Posts: 8
Thanks Alan,

I will follow your recomendations.

Many thanks for support.


Wed Sep 19, 2012 7:43 pm
Profile
Wideband Wizard

Joined: Tue Jun 10, 2008 2:53 am
Posts: 241
Location: Toronto Canada
The Brand is the PLX SMARF Gen 1, they have the gen 2 out which I have never taken a look at.

The SMAFR Gen1 runs the current drive to the sensor pump cell at ~8v, the microcontroller is either running at 5v or 3.3v.

It is not a bad idea, you do get faster response times.

The pump current going into and out the pump cell represents the Lambda of exhaust gas, usually you run the pump current through a 62 ohm resistor and measure the voltage on both end with you ADC to measure the pump current. So in the SMARF case they will need 2 voltage dividers on each end of the 62 ohm resistor to bring voltages down to the ADC range, that is 4 resistors, they probably use 1% tolerance resistors, that might translate to a potential error of around 4%. Other voltage dividers might also be needed on reading the nermest cell voltage, I have not thought so far ahead yet.

All these voltage dividers will contribute linear gain errors, but that is very easy to calibrate out, at the factory they probably have a testing jig that feeds precision voltages to the some port on the SMAFR PCB and calibrate out the linear gain errors, well I am giving them the benefit of the doubt that they do that.

_________________
www.14Point7.com


Last edited by toalan on Thu Sep 20, 2012 2:25 am, edited 1 time in total.



Wed Sep 19, 2012 9:35 pm
Profile WWW
Moderator
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 15204
Location: Home sweet home!
I always enjoy reading your posts! :-)

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Wed Sep 19, 2012 10:10 pm
Profile WWW
TO220 - Visibile

Joined: Mon Dec 31, 2012 2:02 pm
Posts: 12
Perhaps to get you started one might want to look at the datasheet for Bosch's own IC used in their ECUs (road and motorsport) to interface with their LSU4.x sensors.

http://www.bosch-semiconductors.de/medi ... t_Info.pdf

It has a good page about the internal circuitry of th chip.

The IC is the CJ125, a newer version has been announced but is practically impossible to get hold of...


Mon Dec 31, 2012 2:10 pm
Profile
Moderator
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 15204
Location: Home sweet home!
Thanks! I read your sign up details, and removed you from n00b group. Go nuts! :-)

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Mon Dec 31, 2012 4:37 pm
Profile WWW
TO220 - Visibile

Joined: Mon Dec 31, 2012 2:02 pm
Posts: 12
Fred wrote:
Thanks! I read your sign up details, and removed you from n00b group. Go nuts! :-)


Ah, I wondered why my other posts didn't need approving - cheers Fred! I'm using the CJ125 IC in the project I mentioned in sign up details, it's absolutely brilliant as one of my biggest specification constraints in PCB size, so having everything in one tiny SMD package is a god send. One problem, I ordered 3 and by the time I'd paid postage from the states (seems Future Electronics is the only place to get them) it cost me £30!


Mon Dec 31, 2012 7:34 pm
Profile
TO220 - Visibile

Joined: Tue Feb 05, 2013 7:21 pm
Posts: 4
Location: Hungary, Eu.
Hi Guys,

could you help me out with some theoretical/practical doubts I’m having about controller design? I'm putting together a lambda probe controller of my own (not for production/resale), but I'm not that good with electronics. I'm not a complete noob, but I don't have anywhere near the insight of a professional HW designer. Nor do I know the ins and outs of this sensor as well as a lot of you seem to know.
(There's already some design discussion going on here, so I thought I wouldn't open a new thread with my questions, but feel free to move it, if it's too off-topic.)

What I'm planning is nothing new:
- 5V system, with 2.5V bias
- DAC for pump current, voltage feedback via 61.9 ohms resistor to ADC
- superposing an AC coupled 5V PWM onto the Nernst, AC coupling it back out to ADC for Ri measurement

I'm looking to use the PSoC 5, series 5, with 1 x 20bit ADC and 2 x 12bit ADC, some DACs and R2R opamps.

What I’m not really sure about:

1. Rectify Ri (internal resistance) measurement AC voltage before ADC?
Should the signal after AC coupling be rectified with a precision rectifier, or would it be enough to just feed it directly into the ADC, and find the peak-to-peak voltage from the samples via SW?

2. Comparator or ADC for Vs (Nernst voltage) measurement?
Do I need the actual realtime value of Vs, or would it be enough if I fed it into a 450mV comparator, and then step the pump current DAC up/down by one, depending on the comparator output?
I'm guessing it all depends on the response times of the involved elements. The comparator->SW->DAC chain is in the microsecond range, so I’m thinking, it would be fast enough even for individual cylinder AFR measurement, by 3 magnitudes. Or is there something I’m not thinking of?

What I don’t know anything about, though, is the response time of exhaust gas composition to pump current change, or Nernst response to exhaust gas composition change.

3. Which ADC should I use for what, in your opinion?
There are 3 voltages to be measured, pump current resistor V drop, Nernst voltage, Vri. I’d like to measure also MAP, IAT, and EGT/CJT in the meantime, so one channel would have to be multiplexed.

I would have 3 ADCs:
- 1 20-bit, 700ksps
- 2 12-bit, 192ksps

I’m guessing I’d need the high-resolution, high speed ADC for the smallest voltage, which is the Ri AC. But again, this is the only voltage I do not need to measure continuously (1/s enough?), so this is the one I could share with other sensors. Pump current and Vs would have their dedicated 12-bit ADCs. Does this sound right?

4. Maximum permissible AC current on Nernst
The Bosch datasheet says 250uA. What I couldn’t find in it, is what this means. Half peak? Peak-to-peak? RMS? The megamanual PWC site says it’s half peak (500uA p-t-p). But I don’t know, where they got this info from. It would be nice to read it in some official form.

5. Turbo + Individual cylinder AFR measurement (ICAFRM, I’m tired of typing it out :) )
This is more of a theoretical question, I'm not planning anything like that just now. :) Would a turbo interfere with ICAFRM on an I4? How about an I4 with a divided/twinscroll manifold and turbine housing? How about an I6 with or without twinscroll? Would cylinder impulses be smeared together because of the turbo, or only delayed? Does anyone have experience?
Is there a lambda sensor at all, that has the necessary response time from start of diffusion to 450mV to be able to pull off ICAFRM, provided there’s a fast enough controller?

Sorry for the long winded post, I tend to compile my questions into bigger blocks. I like to have a general undestanding about what I don't understand first.

Thank you in advance for any insight!


Tue Feb 12, 2013 3:12 pm
Profile
Moderator
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 15204
Location: Home sweet home!
I have no answers for any of your questions, however I have a question of my own:

If you were to use a multiplexer on your ADC, say the 20bit one, wouldn't you lose some (a lot of?) accuracy in that process?

Hopefully Alan pipes up and helps you out. Those are pretty specific questions :-)

Fred.

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Tue Feb 12, 2013 6:41 pm
Profile WWW
TO220 - Visibile

Joined: Tue Feb 05, 2013 7:21 pm
Posts: 4
Location: Hungary, Eu.
Fred wrote:
If you were to use a multiplexer on your ADC, say the 20bit one, wouldn't you lose some (a lot of?) accuracy in that process?
Fred.

Actually, I don't know, but it's definitely a good point. The PSoC does not have dedicated ADC pins, but relies on an internal bus/switch-matrix to route almost any pin to any internal module, so any signal would have to go through this multpilexing network that to get to an ADC. My guess would be, that this was considered in the design of the PSoC, and accuracy should not suffer. Well, at least not from having to go through the internal multiplexing. Making changes to the routing on the fly could be an entirely different matter, though. I'll dig into the datasheet to find out.

If it does influence accuracy, I guess I could still use an internal R2R opamp to scale it up some, before routing it to the ADC. If that doesn't open up a new can of worms.


Tue Feb 12, 2013 7:30 pm
Profile
Moderator
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 15204
Location: Home sweet home!
Apologies, I had assumed that you meant out-board multiplexing.

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Tue Feb 12, 2013 9:43 pm
Profile WWW
Display posts from previous:  Sort by  
Reply to topic   [ 33 posts ]  Go to page Previous  1, 2, 3, 4  Next

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software for PTF. ColorizeIt.